To a certain extent, the whole body is involved in thinking. The cells of the nervous system respond to the total state of the entire body. A “state of mind” is actually “a state of total conditions.” It is for this reason that fatigue, drugs, and sluggishness caused by inadequate exercise cannot be omitted from a rationale on how to study. Observing the effects of extremes of fatigue, alcohol, and bed-ridden inactivity leaves no doubt that they influence thinking. But many people falsely assume that there is an all-or-nothing situation involved: that before fatigue takes effect, one has to be near a state of exhaustion! How much effect a degree of fatigue or lack of normal exercise has upon mental functioning is not adequately recognized.
As mentioned earlier, the nervous system is composed of the sense-organs, brain, spinal cord, and nerve-bundles of neurons. Complex layers and masses of neurons are located in the brain where higher controls are exerted. The tapering rod of tissues running down the backbone and known as the spinal cord carries fibers of the neurons to and from the brain, as well as possessing local, connecting, reflex switching-centers. In addition, there are thousands upon thousands of extremely thin, wire-like neurons running between the organs and skin and central system. Besides these, there are the familiar sense organs in the head (eyes, ears, etc.) and less-familiar receptors in the joints and other internal organs reporting on the state of affairs within us.
The billions of neurons in this system are marvelously and uniformly arranged from person to person. They are amazingly well organized into patterns of pathways, even before the infant is born. They do not react exactly and uniformly from person to person, however, because one’s own history of experience creates various differences in the pathways followed by impulses. The differences in our personalities are due, in part, to the various differing pathways ingrained in us by our varied experiences.
Each neuron is composed of a cell body with a brush of short, hair-like strands (dendrites) extending from the surface, and a long, thread-like “axon” extending from one end.
In the drawing, A is a typical long neuron (neural cell) found by the millions in the body, gathered into bundles in some regions (cable-like nerves), and capable of carrying electrochemical changes (depolarizations) along the axon. Note the several areas-of-nearness (synapses) which bring electrochemical changes in from other neurons. At the synapses, there are permissions or refusals, as the case may be. Once the message jumps, it can go the whole length of the neuron. The end of the line is a small area of muscle or a small area of a gland. B represents a ganglionic cell in the brain with tiny cell terminals shown close to the cell body. Messages coming in can jump across if enough of the terminals are involved (it is believed), and the message continues along in the ganglionic cell through the axon to some other ganglionic (or other) cell. About ten billion cells of various kinds are located in the brain. At the right is a representation of the shape of the synapse in this case (B’ and B”)-C shows a close-up of the way two axons from two neurons at the left (only the end of the axons showing) come close to the dendrites of another neuron (cell body and nucleus showing). The synapse is shown as discshaped, and is diagramed separately at the extreme right (C”).
The long axons of the neurons entering and leaving the spinal cord and running in from sense organs or out to muscles and glands connect with every part of the body. In the brain, most of these cells are quite short by comparison. The neurons all connect with each other across bridges which are not fully formed. In other words, between any two neurons, an area-of-nearness (but not total connection) is present.The tiny brushes of two neurons are very close, but do not actually touch. Between the dendrites of one neuron and the axons of the nearby contributing neurons, this area-of-nearness is of extreme importance in the process of learning, thinking, and behavior. Due to conditions in this area — a region called the synapse — an impulse may cross if favored, or not cross if not favored. What controls the favoring (facilitation) or not favoring (inhibition) seems to be, in “part, the presence of still other neurons which have grown their processes into the same area. These neurons can instantly create a “set” in the synapse. In a way, these additional neurons give a green light to the passage of an impulse or halt it, according to the influence of past events, stored in some way by the controlling neurons or neuron complexes elsewhere in the brain. Past training, readiness or “set,” and other factors such as rest and health may precondition the area-of-nearness.
Repetitions whereby impulses pass again and again seem to make it easier each time for that kind of impulse to pass over the bridge. Obviously, if we can train the cells which control the jumping across of the “right” impulses to bring about intelligent behavior or clear thinking, we can rise above our blunders and our incorrect reactions to things. The business of self-education is centered upon the training of many of these billions of bridges or synapses. Each person has had slightly differing training with regard to the controls in these areas-of-nearness. The great variations of people’s experience and their powers of control at this level are partly responsible for the great variations in our total “personality” and reactions to the world around us.